TaskExecutor implementation that delegates to a CommonJ WorkManager,
implementing the WorkManager interface,
which either needs to be specified as reference or through the JNDI name.

This is the central convenience class for setting up a
CommonJ WorkManager in a Spring context.

Also implements the CommonJ WorkManager interface itself, delegating all
calls to the target WorkManager. Hence, a caller can choose whether it wants
to talk to this executor through the Spring TaskExecutor interface or the
CommonJ WorkManager interface.

The CommonJ WorkManager will usually be retrieved from the application
server's JNDI environment, as defined in the server's management console.

Note: At the time of this writing, the CommonJ WorkManager facility
is only supported on IBM WebSphere 6.0+ and BEA WebLogic 9.0+,
despite being such a crucial API for an application server.
(There is a similar facility available on WebSphere 5.1 Enterprise,
though, which we will discuss below.)